The present invention relates to semiconductor test systems and more particularly to an apparatus for connecting an integrated circuit device to such a test system.
Semiconductor test systems are used for testing integrated circuit (IC) devices to verify their performance characteristics In a typical test system, the IC device is placed in a test fixture that is mounted on a device under test (DUT) board. The DUT board has contact pads that are electrically connected to the individual leads of the IC device. Electrical signal probes from the tester are brought into contact with the contact pads on the test board for coupling electrical signals to the IC and for monitoring the signals from the IC.
The LT1000 Semiconductor Test System, manufactured by Tektronix, Inc., Beaverton, Oreg., and the assignee of the present invention, is an example of a semiconductor test system for testing digital IC devices. The LT1000 has a test head for accepting IC devices and a host controller for controlling the transmitting, receiving and processing of signals to and from the IC device under test. The test head has a device under test (DUT) board onto which the IC device is placed. The DUT board has electrically conductive runs leading from the IC and terminating in plated through holes in the board. The through holes in the DUT board are formed in a linear pattern radiating from a central vertical axis of the board. On the opposite side of the DUT board, the plated through hole patterns are electrically connected to electrical test pads that are in a similar linear radiating pattern from the center of the DUT board as the through holes. Mating with the contact pads of the DUT board are spring loaded electrical probes that are connected to pin cards.
The pin cards are arranged on edge in the test head with the cards in a radiating pattern from the center of the test head. The spring loaded probes are mounted in a fixture that is secured to the pin card board. The probes are directly soldered to conductive runs on the card. An electrical interface is provided in the test head for connecting the pin cards to the host controller.
The LT1000 is designed for testing digital IC devices having pin counts from 64 to 256 pins. The number of pin cards used in the test head depends on the pin count of the device being tested. In use, an IC test fixture is mounted on the DUT board for accepting the IC device. The DUT board is designed to accept any IC having a pin count from 64 to 256 pins. A locking mechanism on the test head lowers the DUT board onto the spring loaded probes of the pin cards and locks the board in place. Electrical connectivity from the IC device to the host controller is via the conductive runs on one surface of the the DUT board, the plated through holes, the test pads on the opposite side of the board, the spring loaded probes, the electronic circuitry on the pin cards, the pin card interface, and through umbilical cables from the test head to the controller.
With the development of IC devices that process both digital and analog signals on the same chip, there is a need for a semiconductor test system that can couple both type of signals to and from IC device. However, existing spring loaded probe technology does not provide the necessary signal isolation and impedance matching that is necessary for such testing. In addition, isolation is needed between the digital and analog signals on the circuit boards used in such a system.
To provide the isolation and impedance matching necessary for mixed signal testing of IC's, a coaxial probe is necessary. One example of a coaxial probe is described in U.S. Pat. No. 4,588,241 to Ardezzone. Ardezzone describes an electrical signal probe mounted in a mounting block and having both a movable central conductor and a cylindrical shield conductor electrically insulated from the central conductor. The central conductor of the Ardezzone probe is connected to a central conductor of a coaxial cable and the cylindrical shield conductor is connected to the outer shielding conductor of the cable. A disadvantage of the Ardezzone probe is the difficulty in repairing and replacing defective probes. The coaxial cable electrically connecting the probe to the circuit board must be unsoldered and the probe and the securing means, such as a "C" ring, removed from the probe body before the probe is completely removed from the fixture holding it. Repairs of this type are time consuming in an environment where up to 256 probes are use for testing a device.
What is needed is a semiconductor test system for testing IC devices in a mixed analog and digital signal environment. The system should provide isolation between the analog and digital signals in the test system while at the same time providing ease of serviceability and repair.